Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

664
FXUS63 KLOT 111053
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
553 AM CDT Thu Jun 11 2026

.KEY MESSAGES...

- Another round or two of severe storms are expected today with
  the period of greatest threat between 4 and 11 PM. All
  hazards (tornadoes, destructive winds, destructive hail) are
  possible across the entire area.

- In particular, there is a threat for strong to intense
  tornadoes this evening (4 to 8 PM) especially along and north
  of Interstate 88.

- After a dry and cooler day on Friday, there is another threat
  for severe weather on Saturday.

&&

.UPDATE...
Issued at 553 AM CDT Thu Jun 11 2026

Over the past few hours, a compact MCS has emerged across far
southwestern Iowa. Per recent KOAX radar data, the system is
highly organized with signs of a hybrid cold pool/gravity wave
along the leading edge supporting measured severe wind gusts.
While CAM-based guidance has been insisting that the MCS will
turn northeasterly early this morning, it has instead remained
on a due easterly trajectory. As a result, am starting to wonder
if it will just plow eastward and through the heart of the
forecast area later this morning rather than along and north of
Interstate 80 (still looking like an arrival time near the I-39
corridor in the 10am to 12pm timeframe).

Should a further south track of the convective system verify
into the early afternoon hours, would have to think that rapid
airmass recovery may be stunted with northward extent and the
warm front may instead verify closer to I-80 or I-88 in time for
the second round of storms. If this were to occur, the main
tornado threat area could end up further to the south than
previously thought. At the same time, could envision the
strongest instability being modestly offset from the strongest
low-level shear this evening potentially mitigating a higher-end
tornado scenario. These are the type of details that come into
closer detail in the hours before the event.

At this point, did increase PoPs both in areal coverage and
actual values across much of the area in the 11 am to 3 pm time
window with the expectation for the first round of storms to
move through more of the area rather than just the northern
half. Trends will continue to inform later forecast updates.

Borchardt

&&

.DISCUSSION...
Issued at 304 AM CDT Thu Jun 11 2026

     THREAT FOR STRONG TORNADOES AND DESTRUCTIVE WINDS IN THE
REGION THIS AFTERNOON AND EVENING...

Early morning water vapor imagery depicts broad aggregate
upper-level troughing centered on the northern Plains. Several
embedded short-wavelength troughs are parading around the
perimeter of the broader trough, including a notable impulse
moving across central Wyoming at press time. Per recent
mesoanalysis data across the central Plains, the impulse has
already led to the development of a lee cyclone centered in
western Kansas. Meanwhile, a broad region of warming cloud tops
extends across the Lower Great Lakes associated with a
gradually-decaying mesoscale convective system. Per a recent
surface analysis, outflow from the convective system has
(temporarily) displaced a warm frontal zone southward, with the
boundary currently stretching from central Indiana through
south-central Illinois and northeastern Missouri. Between both
large-scale features, convection is developing across southern
Nebraska associated with presumably a mid-level gravity wave
originating from unbalanced upper-level flow (a notable 75kt jet
streak is departing the base of the aforementioned Wyoming
shortwave). Indeed, am noting the hallmarks of developing
gravity wave associated convection (GWAC) along the I-80
corridor in Nebraska at press time.

As the Wyoming shortwave ejects east-northeastward into the
Great Lakes this morning, the southern Plains low will rapidly
shift northeastward from near Kansas City, Missouri toward
central Iowa. Ahead of the surface low, the developing
convection in southern Nebraska is expected to intensify and
consolidate into a compact mesoscale convective system or GWAC
supercell complex and track east-northeastward toward the
Mississippi River and eventually into northern Illinois. It is
unclear if the convection would ultimately become surface-based
as the boundary layer warms and synoptic warm front retreats
northward (more on this soon), though the presence of steep mid-
level lapse rates (contributing to MUCAPE > 2000 J/kg) and
increasing shear profiles (effective shear in excess of 50 kt)
will support a threat for destructive winds (>70 mph) and hail
(>2" in diameter) with the first round of storms. The time
window for the early-day storms looks to be generally between 11
AM and 3 PM, mainly north of Interstate 80. (Am somewhat
skeptical of CAM guidance depicting early-afternoon convection
decaying while approaching Lake Michigan).

Later this afternoon and evening, ensemble model guidance
remains in agreement that the surface low will deepen toward the
lower to mid 990s mb range while lifting into central
Wisconsin. Intensifying south to southwesterly flow on the
southeastern side of the surface low will lead to rapid airmass
recovery across northern Illinois as well as the advection of an
EML plume back into the Lower Great Lakes. CAM-based guidance
suggests that dew points in the warm sector will soar into the
mid to locally upper 70s this afternoon, apparently a
consequence of evaporation of water from the heavy rain
yesterday evening and early this morning to our south and west.
Resulting mean 1km mixing ratios nearing 19 g/kg and mid-level lapse
rates of around 8 K/km will contribute to MLCAPE of locally 3500
J/kg in the warm sector. At the same time, low- to upper-level flow
will rapidly intensify across the warm sector during the afternoon
and evening leading to strong deep-layer shear profiles.

Thunderstorms appear poised to develop across central Iowa by
mid-afternoon and then expand in coverage and increase in
intensity while moving toward northern Illinois and southern
Wisconsin this evening and eventually northwestern Indiana after
sunset. Given the degree of strong forcing, strong instability,
and high moisture values, a somewhat messy storm mode is
expected with a mix of high-precipitation supercells and line
clusters eventually merging into a squall line with a threat
for all hazards (tornadoes, destructive winds, and wind-blown
damaging hail). The main time window for severe weather this
evening appears to be from 4 to 11 PM.

Am quite concerned in a relatively narrow west-to-east zone
favorable for strong to intense tornadoes (EF-3+) somewhere
across southern Wisconsin or northern Illinois particularly
between 4 and 8 PM. Forecast soundings along the warm front this
evening depict a rare and volatile combination of exceptional
instability augmented by locally pooled moisture (MLCAPE >4000 J/kg)
and intense low-level shear (350 J/kg of 0-1km SRH for eastward-
moving storms, nearly all of characterized by streamwise horizontal
vorticity), leading to effective STP values in the double-digits.
Pinpointing the eventual location of the warm front will be
paramount to identifying the zone of greatest tornado potential
today with reasonable outcomes ranging from the front stalling near
Interstate 88 in northern Illinois to the I-94 corridor in southern
Wisconsin (consensus is near the Wisconsin state line). Such a
threat for strong to intense tornadoes is contingent on a supercell
storm mode being maintained, though the degree of low-level shear
would still support strong QLCS tornadoes near the warm front.

Just want to conclude by saying that environments supportive of
strong to intense tornadoes often have many off-ramps and are
accordingly never a guarantee. Will the warm front surge
well north of our area taking the primary tornado threat with it?
Will the morning storms suppress the warm front south, or not allow
for rapid destabilization ahead of the cold front? Will storm mode
remain far too messy to sustain strong low- level rotation and
tornadoes? Or, will there be a discrete supercell that latches onto
the warm front draped across our area? These factors are essentially
noise within the broader signal to craft a forecast and can only be
determine as an event is unfolding (sometimes literally just an hour
or two beforehand). Taken altogether, today is a day to stay very
connected to the forecast and to ensure you have multiple ways to
get warning information for the off chance that the dominoes do end
up falling in the wrong direction in our area.


Friday onward:

A brief break in the pattern is expected on Friday with
noticeably lower humidity values and temperatures. Broad upper-
level cyclonic flow will remain across the northern United
States through the weekend and beyond, maintaining periodic
opportunities for showers and thunderstorms. Will note another
threat for severe weather on Saturday as a more notable
shortwave and associated cold front moves into the Great Lakes
and interacts with a narrow EML plume and low- level moisture
return. At first glance, the main threats on Saturday should be
damaging hail and damaging winds.


Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1211 AM CDT Thu Jun 11 2026

Aviation forecast concerns for the 06Z TAFs:

- Area of SHRA/embedded TSRA ending for CHI terminals 07-08Z.

- A period of TSRA possible late morning into early afternoon
  across far northern IL, with highest likelihood at KRFD. Did
  add PROB30s for all CHI metro sites except GYY, where
  potential decreases with southeastward extent.

- Higher probability (80%) for a line of severe thunderstorms
  late afternoon into mid-evening ahead of a cold front. All
  severe threats possible.

- Period of strong southerly winds expected Thursday
  afternoon/evening, with gusts AOA 30 kts possible. Winds shift
  west and remain breezy behind cold front Thursday evening.

Second round of thunderstorms has largely pushed south/southeast
of the terminals as of midnight, though an area of rain with
embedded lightning continues to track east across the area in
association with a convectively-induced mid-level circulation.
This should end from west to east across the Chicago terminals
between 07-08Z. Relatively quiet conditions are then expected
overnight into Thursday morning with modest south-southwest
winds, though there continues to be support in some model
guidance for MVFR ceiling development around sunrise. Confidence
in coverage of this remains low at this time, though have
maintained a SCT015 mention which can be updated to ceilings if
necessary.

An increasing model signal persists for a late morning/early
afternoon round of thunderstorms across far northern IL. Highest
probabilities (~60%) is at KRFD toward midday, with probs
decreasing to ~30% for the Chicago metro sites early in the
afternoon. Have included a TEMPO at KRFD, and PROB30 mentions
for this at KORD/KDPA/KMDW. Likelihood decreases farther
southeast and have left out for KGYY. A more widespread
thunderstorm threat then looks to develop late Thursday
afternoon and evening, with a line of severe storms expected.
Some timing differences remain in guidance, though general
agreement suggests a few hour period starting around 22Z for
KRFD and 00Z for Chicago sites. All severe modes possible,
especially damaging winds.

Ahead of the squall line, synoptic winds are expected to back
south or even slightly south-southeast in the afternoon and
strengthen. Gusts at or above 30 kts are possible (with some
high-res model guidance even 40+ kts late - though not quite
confident enough to go that high at this distance). Surface
winds will shift westerly with the passage of the cold front
Thursday evening, likely remaining breezy around 25 kts for a
time into the night.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 PM this afternoon to 10 PM CDT
     this evening for the IL and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago